Date: Fri, 3 May 2019 12:09:00 +0200 From: Borja Marcos <borjam@sarenet.es> To: Pete French <petefrench@ingresso.co.uk> Cc: freebsd-stable@freebsd.org Subject: Re: ZFS... Message-ID: <C5403ADD-86C1-4184-BDA6-DA8C7426458E@sarenet.es> In-Reply-To: <cde21bb4-d741-3300-077f-745cfc343aa9@ingresso.co.uk> References: <30506b3d-64fb-b327-94ae-d9da522f3a48@sorbs.net> <CAOtMX2gf3AZr1-QOX_6yYQoqE-H%2B8MjOWc=eK1tcwt5M3dCzdw@mail.gmail.com> <56833732-2945-4BD3-95A6-7AF55AB87674@sorbs.net> <3d0f6436-f3d7-6fee-ed81-a24d44223f2f@netfence.it> <17B373DA-4AFC-4D25-B776-0D0DED98B320@sorbs.net> <70fac2fe3f23f85dd442d93ffea368e1@ultra-secure.de> <70C87D93-D1F9-458E-9723-19F9777E6F12@sorbs.net> <CAGMYy3tYqvrKgk2c==WTwrH03uTN1xQifPRNxXccMsRE1spaRA@mail.gmail.com> <fe6880bc-d40a-2377-6bea-28bfd8229e9f@sorbs.net> <58DA896C-5312-47BC-8887-7680941A9AF2@sarenet.es> <cde21bb4-d741-3300-077f-745cfc343aa9@ingresso.co.uk>
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> On 3 May 2019, at 11:55, Pete French <petefrench@ingresso.co.uk> = wrote: >=20 >=20 >=20 > On 03/05/2019 08:09, Borja Marcos via freebsd-stable wrote: >=20 >> The right way to use disks is to give ZFS access to the plain CAM = devices, not thorugh some so-called JBOD on a RAID >> controller which, at least for a long time, has been a *logical* = =E2=80=9CRAID0=E2=80=9D volume on a single disk. That additional layer = can >> completely break the semantics of transaction writes and cache = flushes. >> With some older cards it can be tricky to achieve, from patching = source drivers to enabling a sysctl tunable or even >> flashing the card to turn it into a plain HBA with no RAID features = (or minimal ones). >=20 > Oddly enough I got bitten by something like this yesteray. I have a = machine containing an HP P400 RAID controller, which is nice enough, but = I run ZFS so I have made the drives all into RAID-0 as being as close as = I can get to accessing the raw SAS drives. >=20 > BSD seems them as da0, da1, da2, da3 - but the RAID controller oly = presents one of them to the BIOS, so my booting has to be all from that = drive. This has been da0 for as long as I can remember, but yesteday it = decided to start using what BSD sees as da1. Of course this is very hard = to recognise as da0 and da1 are pretty much mirrors of each other. Spent = a long time trying to work out why the fixes I was applying to da0 were = not being used at boot time. Hmm What happens when you do a =E2=80=9Ccamcontrol devlist=E2=80=9D? Camcontrol tags da0 -v? How is the controller recognized by FreeBSD? For some of them it=E2=80=99s= possible to instruct the controller to present the physical devices to = CAM. Of course you need to be careful to avoid any logical volume configuration in that = case.=20 But I would only tinker with this at system installation time, making = such a change on a running system with valid data can be disastrous. For mfi recognized cards there is a tunable: = hw.mfi.allow_cam_disk_passthrough For aac cards it was a matter of commenting a couple of source code = lines in the driver (at your own risk of course). I=E2=80=99ve been = running a=20 server for years doing that. Borja.
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